The present invention relates to a fluid clutch for transmitting rotational torque of an internal combustion engine.
A friction clutch, a fluid coupling and a torque converter have generally been used as clutches for transmitting the rotational torque of internal combustion engines.
The friction clutch comprises a flywheel mounted on a crank shaft of an engine, a pressure plate having a clutch facing disposed opposite the flywheel, and a clutch driven plate that is disposed between the flywheel and the pressure plate and is mounted on an input shaft of a transmission arranged on the same axis as the crank shaft. The transmission of torque is controlled by adjusting the pushing force exerted by the pressure plate.
The fluid coupling and torque converter comprise a casing coupled to a crank shaft (input shaft) of an engine, a pump that is disposed opposite casing and is mounted on the casing, a turbine that is disposed in a chamber formed by the pump and the casing so as to be opposite the pump and that is mounted on an output shaft arranged on the same axis as the crank shaft (input shaft), and an operation fluid filling a pump chamber. In the thus constituted fluid coupling and torque converter, a centrifugal force acts on the operation fluid in the pump due to the rotation of the pump, and the operation fluid that flows to the outer peripheral side due to the centrifugal force is permitted to flow into the turbine from the outer peripheral side thereof, thereby to drive the turbine.
Here, the friction clutch has a clutch facing that is subject to be worn out. After being used for a predetermined period of time, therefore, the friction clutch must be renewed. Besides, it is difficult to control the torque in the case of automatically controlling the clutch.
In the fluid coupling and torque converter, the pump on the drive side and the turbine on the driven side are not in mechanical contact with each other and, hence, are not subject to wearing out. However, it is not possible to freely control the transmission of torque. Besides, since the torque is not transmitted unless there is a difference in the rotational speed between the pump and the turbine, the transmission of torque becomes zero (0) when the ratio of the rotational speed of the pump to the turbine is nearly 1. When the fluid coupling and torque converter are used for a drive device of a vehicle, a drag torque is produced due to its nature in a state where the vehicle is at rest, the engine is running and a speed change gear of the transmission is in mesh, i.e., in a state where the input shaft is revolving but the output shaft is at rest. The drag torque, in general, stands for a torque that is transmitted in a state where the engine is in operation at an idling speed. The drag torque increases to a considerable degree when a design point of the fluid coupling and torque converter is set to be a rotational speed ratio at which a maximum efficiency is obtained, i.e., is set to be a rotational speed ratio of the pump to the turbine of from about 0.95 to about 0.98. When the drag torque is great, the idling operation of the engine loses stability to a conspicuous degree, and this unstable rotation becomes a cause of abnormal vibration in the drive system. Besides, a large drag torque is detrimental to the fuel efficiency during the idling operation.
It is an object of the present invention to provide a fluid clutch which is capable of easily controlling the transmission of torque and which is not so subject to being worn out.
In order to accomplish the above-mentioned object according to the present invention, there is provided a fluid clutch disposed between a first shaft and a second shaft which are arranged on the same axis, comprising:
a casing drive-coupled to said first shaft and having plural pump chambers;
a gear pump having a first pump gear which is disposed in said casing, is drive-coupled to said second shaft, and has a gear formed on the outer periphery thereof, and further having second plural pump gears which are disposed in said plural pump chambers formed in said casing and are in mesh with said first pump gear;
an intake passage that is formed in said casing and in said second shaft and that communicates with an intake port of said gear pump;
an exhaust passage that is formed in said casing and in said second shaft and that communicates with an exhaust port of said gear pump; and
a control valve that is disposed in a valve hole formed in said second shaft, that communicates with said intake passage and with said exhaust passage, and that controls a communication area between said intake passage and said exhaust passage.
It is desired that said intake passage and said exhaust passage communicate with a supplementary passage, and that check valves be disposed between said supplementary passage and said intake passage and between said supplementary passage and said exhaust passage, to permit the flow of the fluid from said supplementary passage to said intake passage and to said exhaust passage.